I don’t have one of them, but I’m guessing you are using one of those less expensive types? I poked around last summer about incubating and saw that some people do keep the incubators in the styrofoam for extra insulation. Also if it’s the overseas ones I’m thinking of, I read the instructions are maybe not the greatest....
I would keep the stryrofoam and run it without hatching eggs to see how well it keeps temp in the location you set it up. You may or may not need it. I am guessing it is one with a built in thermostat? Don’t solely trust the built in thermometer on any incubator! Invest in another (or two or three) thermometer to compare with. Hygrometer, too.